The present invention relates to a device for error detection in a digital signal evaluation unit.
It is known that, in signal evaluation units designed as analog evaluation IC's, for example, monitoring measures are required that allow misoperations to be recognized. Various possibilities for accomplishing this are known. For example, a method for monitoring and error recognition is presented in DE-P 197 560 81.4 that is carried out in an analog evaluation IC in conjunction with knock detection in an internal combustion engine. With this knock detection, the structure-borne noise signals supplied by the knock sensors are forwarded to the evaluation IC via a multiplexer. This IC is composed, at the least, of an amplifier, a filter, a rectifier, and an integrator. The resultant integrator result is used as the result of knock detection in order to calculate a knock index for the knock control. Signal evaluation takes place in this IC in analog form. Two test options are implemented to monitor the operatability of the integrated circuit (IC). These test options are referred to as test pulse and zero test. Using this type of diagnosis, the entire signal path except for the multiplexer can be checked for operatability.
In the first test option—the test pulse—a test signal is supplied to the evaluation chain after the multiplexer. The downstream integrator is fully modulated by means of this signal in a relatively short period of time, independently of the amplifier level setting. If it is recognized that the expected full modulation of the integrator has not occurred after a relatively short period of time, an error is detected. In the second test option—the O-test—the signal path is separated after the multiplexer. In this case, only the disturbing noises, e.g., background noises, occurring internally in the integrated circuit (IC) are integrated in the integrator.
The signal available in the integrator then provides information as to whether erroneous disturbances have occurred, or if any other misoperations are present. The integrated circuit for evaluation of knock signals in an internal combustion engine must be monitored, since, if the evaluation circuit would fail, erroneous values for knock control would be provided and the knock control itself would no longer function correctly, and damage could occur to the internal combustion engine.
New units for signal evaluation, e.g., in conjunction with knock detection in internal combustion engines, have digital evaluation IC's. The entire signal evaluation, if possible, is thereby performed with the aid of a digital arithmetic and logic unit. Such an evaluation IC designed to evaluate the output signals of knock sensors is described in patent application DE-P 100 041 66.3. In this type of digital signal evaluation, a typical property, e.g., components typical for knock, are extracted from the conditioned and digitized output signals from the sensors, and they are compared with specifiable threshold values for knock detection. A checking or monitoring of the operatability of the IC is not performed in this digital signal evaluation described in DE-P 100 041 66.3.